The plaza is an underused urban room that genuinely activates when something's happening in it. The Red Umbrellas artist showcase is visual and street-level, meaning you can walk through it rather than stand in front of it. Sunday Fun Days leans casual — more neighborhood-hangout energy than programmed festival. Also worth knowing: the Cube of Truth crew from Anonymous for the Voiceless sets up here on weekend afternoons on a semi-regular basis — it's a stationary street-activism format with masked participants and folks available to talk. Not a march, not a blockade. If you see it, you'll recognize it.

Practical note: Union Square has paid parking in the underground garage directly beneath the plaza (enter on Geary), but on weekends the Powell Street BART exit puts you at the plaza steps in under a minute. Skip the car.

If you've got two hours: walk through whatever the artist showcase has up, circle the plaza once to see what's running, then cut down Post to the Tenderloin edge for food before heading back for the afternoon programming.